Historically, the recovery of pencillins from the whole fermentation broth has included, as the primary purification step, a solvent extraction of the penicillins directly from the filtered fermentation broth. Both theory and practice (especially under controlled laboratory conditions) have shown this procedure to be highly efficient and selective.
In the case where the penicillins produced in the fermentation are stable to acid, the fermentation broth is adjusted to an acid pH before the extraction with the organic solvent. The acid-stable penicillin present in the organic phase is then transferred to an aqueous buffer solution, from whence it can then be crystallized by salting out of solution with a salt such as potassium acetate.
This remarkable stability to acids displayed by certain penicillins has long been known in the art. Brandl et al., U.S. Pat. No. 2,756,226 (July 24, 1956), teach that these penicillin acids can be recovered from an aqueous solution of their salts simply by acidifying the solution and filtering off the solid crystalline penicillin acid which precipitates. Among the acids disclosed in this reference is phenoxymethyl penicillin, i.e., penicillin V. German Pat. No. 1,131,677 teaches the purification of phenoxymethyl penicillin, as an alkali of ammonium salt, by acidification with excess of acetic acid to give yields of up to about 90 percent of the pure penicillin acid. Further, Baker, U.S. Pat. No. 3,904,605 (Sept. 9, 1975), discloses a process for preparing penicillin sulfoxides starting with penicillin-containing, filtered fermentation broth. After formation, the penicillin sulfoxide is precipitated by the addition of acid.
The separation of a penicillin in the form of its potassium salt from a butyl acetate extract of filtered fermentation broth, by the addition of a 20% solution of anhydrous potassium acetate in methanol, is disclosed by U.S. Pat. No. 3,461,116 (Aug. 12, 1969), and U.S. Pat. No. 3,502,655 (Mar. 24, 1970).
It is well-known to those skilled in the penicillin art that conventional extraction procedures involving water-immiscible solvents are multi-step, and, in general, costly to operate. The presently disclosed process overcomes this disadvantage of the older method.
Another advantage of the instantly disclosed novel process is that the inention makes it possible to process fermentation broths which contain large excesses of residual precursor. The precursor in the case of penicillin V is phenoxyacetic acid, usually employed as the sodium salt. The acidification process also assits in removing insolubles and mycelial solids, some amorphous and microcrystalline substances, and in the case of penicillin V, an impurity identified as p-hydroxy penicillin V, since the latter, together with phenoxyacetic acid, remains in the liquid phase after the acidification.